The invention concerns an indicator chamber (optode) comprising an indicator and a membrane surrounding the indicator and impermeable to it for measurement of concentrations of substance particles by means of e.g. a light measurement system, consisting of a light source, a light receiver and read-out means. In particular, the invention concerns the membrane which surrounds the optode.
The prior art systems operate on the principle that the portion of a composition to be measured is separated from components which disturb the accuracy of measurement. For example, if the oxygen content of blood is to be measured by fluorescence methods, certain protein fractions would render direct readings inaccurate either through their own fluorescence or through binding of the indicator. By separating the measurement area by means of a membrane through which the fraction to be measured may diffuse, blood proteins and other particle fractions are held back, preventing disturbances of the accuracy of measurement.
The disadvantage of the prior art devices lies in the fact that there are only a few types of membranes which exhibit such selective properties; for example, gas/teflon is such a separation pair. The range of applicability of the devices is, therefore, rather restricted. This is in particular unfortunate, in that the method is characterized by a great degree of freedom from side reactions--so that the measurement is not rendered false because of other components--and, in addition, the measurement may be carried out quickly and without special preparation.